Chitiniphilus purpureus sp. nov., a novel chitin-degrading bacterium isolated from crawfish pond sediment.

A novel Gram-stain-negative, curved rod-shaped, motile and chitin-degrading strain, designated CD1T, was isolated from crawfish pond sediment in Caidian District (30° 58' N 114° 03' E), Wuhan City, Hubei Province, PR China. Growth of this strain was observed at 15-40°C (optimum between 28 and 30 °C), at pH 7.0-9.0 (optimum between pH 7.0 and 8.0) and with 0-1 % (w/v) NaCl (optimum at 0 %). With respect to the 16S rRNA gene sequences, strain CD1T had the highest similarity (96.91-97.25 %) to four type strains of the genera 'Chitinolyticbacter' and Chitiniphilus within the family Chitinibacteraceae. The phylogenetic trees based on genome sequences and 16S rRNA gene sequences indicated that strain CD1T was close to members of these two genera, in particular to the genus Chitiniphilus. The genomic DNA G+C content of strain CD1T was 64.8 mol%. The average nucleotide identity and the Genome-to-Genome Distance Calculator results showed low relatedness (below 95 and 70 %, respectively) between strain CD1T and the closely related type strains. Ubiquinone-8 was the predominant quinone. The major cellular fatty acids were C10 : 0, C16 : 0, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The polar lipid profile was composed of a mixture of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, four unidentified lipids, two unidentified phospholipids, two unidentified aminolipids and an unidentified aminoglycolipid. On the basis of the evidences presented in this study, strain CD1T represents a novel species of the genus Chitiniphilus, for which the name Chitiniphilus purpureus sp. nov. is proposed, with strain CD1T (=CCTCC AB 2022395T=KCTC 92850T) as the type strain.

Arsenite Mediates Selenite Resistance and Reduction in Enterobacter sp. Z1, Thereby Enhancing Bacterial Survival in Selenium Environments.

Arsenic (As) is widely present in the environment, and virtually all bacteria possess a conserved ars operon to resist As toxicity. High selenium (Se) concentrations tend to be cytotoxic. Se has an uneven regional distribution and is added to mitigate As contamination in Se-deficient areas. However, the bacterial response to exogenous Se remains poorly understood. Herein, we found that As(III) presence was crucial for Enterobacter sp. Z1 to develop resistance against Se(IV). Se(IV) reduction served as a detoxification mechanism in bacteria, and our results demonstrated an increase in the production of Se nanoparticles (SeNPs) in the presence of As(III). Tandem mass tag proteomics analysis revealed that the induction of As(III) activated the inositol phosphate, butanoyl-CoA/dodecanoyl-CoA, TCA cycle, and tyrosine metabolism pathways, thereby enhancing bacterial metabolism to resist Se(IV). Additionally, arsHRBC, sdr-mdr, purHD, and grxA were activated to participate in the reduction of Se(IV) into SeNPs. Our findings provide innovative perspectives for exploring As-induced Se biotransformation in prokaryotes.

Contributions of selenium-oxidizing bacteria to selenium biofortification and cadmium bioremediation in a native seleniferous Cd-polluted sandy loam soil.

Selenium (Se) is a trace element that is essential for human health. Daily dietary Se intake is governed by the food chain through soil-plant systems. However, the cadmium (Cd) content tends to be excessive in seleniferous soil, in which Se and Cd have complex interactions. Therefore, it is a great challenge to grow crops containing appreciable amounts of Se but low amounts of Cd. We compared the effects of five Se-transforming bacteria on Se and Cd uptake by Brassica rapa L. in a native seleniferous Cd-polluted soil. The results showed that three Se-oxidizing bacteria (LX-1, LX-100, and T3F4) increased the Se content of the aboveground part of the plant by 330.8%, 309.5%, and 724.3%, respectively, compared to the control (p < 0.05). The three bacteria also reduced the aboveground Cd content by 15.1%, 40.4%, and 16.4%, respectively (p < 0.05). In contrast, the Se(IV)-reducing bacterium ES2-45 and weakly Se-transforming bacterium LX-4 had no effect on plant Se uptake, although they did decrease the aboveground Cd content. In addition, the three Se-oxidizing bacteria increased the Se available in the soil by 38.4%, 20.4%, and 24.0%, respectively, compared to the control (p < 0.05). The study results confirm the feasibility of using Se-oxidizing bacteria to simultaneously enhance plant Se content and reduce plant Cd content in seleniferous Cd-polluted soil.

Selenium-oxidizing Agrobacterium sp. T3F4 decreases arsenic uptake by Brassica rapa L. under a native polluted soil.

Toxic arsenic (As) and trace element selenium (Se) are transformed by microorganisms but their complex interactions in soil-plant systems have not been fully understood. An As- and Se- oxidizing bacterium, Agrobacterium sp. T3F4, was applied to a native seleniferous As-polluted soil to investigate As/Se uptake by the vegetable Brassica rapa L. and As-Se interaction as mediated by strain T3F4. The Se content in the aboveground plants was significantly enhanced by 34.1%, but the As content was significantly decreased by 20.5% in the T3F4-inoculated pot culture compared to the control (P < 0.05). Similar result was shown in treatment with additional 5 mg/kg of Se(IV) in soil. In addition, the As contents in roots were significantly decreased by more than 35% under T3F4 or Se(IV) treatments (P<0.05). Analysis of As-Se-bacterium interaction in a soil simulation experiment showed that the bioavailability of Se significantly increased and As was immobilized with the addition of the T3F4 strain (P < 0.05). Furthermore, an As/Se co-exposure hydroponic experiment demonstrated that As uptake and accumulation in plants was reduced by increasing Se(IV) concentrations. The 50% growth inhibition concentration (IC50) values for As in plants were increased about one-fold and two-fold under co-exposure with 5 and 10 µmol/L Se(IV), respectively. In conclusion, strain T3F4 improves Se uptake but decreases As uptake by plants via oxidation of As and Se, resulting in decrease of soil As bioavailability and As/Se competitive absorption by plants. This provides a potential bioremediation strategy for Se biofortification and As immobilization in As-polluted soil.

Comparative efficacy of bio-selenium nanoparticles and sodium selenite on morpho-physiochemical attributes under normal and salt stress conditions, besides selenium detoxification pathways in Brassica napus L.

Selenium nanoparticles (SeNPs) have attracted considerable attention globally due to their significant potential for alleviating abiotic stresses in plants. Accordingly, further research has been conducted to develop nanoparticles using chemical ways. However, our knowledge about the potential benefit or phytotoxicity of bioSeNPs in rapeseed is still unclear. Herein, we investigated the effect of bioSeNPs on growth and physiochemical attributes, and selenium detoxification pathways compared to sodium selenite (Se (IV)) during the early seedling stage under normal and salt stress conditions. Our findings showed that the range between optimal and toxic levels of bioSeNPs was wider than Se (IV), which increased the plant's ability to reduce salinity-induced oxidative stress. BioSeNPs improved the phenotypic characteristics of rapeseed seedlings without the sign of toxicity, markedly elevated germination, growth, photosynthetic efficiency and osmolyte accumulation versus Se (IV) under normal and salt stress conditions. In addition to modulation of Na+ and K+ uptake, bioSeNPs minimized the ROS level and MDA content by activating the antioxidant enzymes engaged in ROS detoxification by regulating these enzyme-related genes expression patterns. Importantly, the main effect of bioSeNPs and Se (IV) on plant growth appeared to be correlated with the change in the expression levels of Se-related genes. Our qRT-PCR results revealed that the genes involved in Se detoxification in root tissue were upregulated upon Se (IV) treated seedlings compared to NPs, indicating that bioSeNPs have a slightly toxic effect under higher concentrations. Furthermore, bioSeNPs might improve lateral root production by increasing the expression level of LBD16. Taken together, transamination and selenation were more functional methods of Se detoxification and proposed different degradation pathways that synthesized malformed or deformed selenoproteins, which provided essential mechanisms to increase Se tolerance at higher concentrations in rapeseed seedlings. Current findings could add more knowledge regarding the mechanisms underlying bioSeNPs induced plant growth.

Fibrisoma montanum sp. nov., isolated from soil of Mountain Danxia, China.

A Gram-stain-negative, non-motile, rod-shaped, aerobic bacterium, designated HYT19T, was isolated from soil of Mountain Danxia in southern China. It showed the highest similarity of 16S rRNA gene sequence (97.0%) and formed a monophyletic clade with Fibrisoma limi BUZ 3T. Strain HYT19T grew at 16-37 °C (optimum 28-30 °C) and at pH 6-7. The draft genome size of strain HYT19T was 7.8 Mb with a DNA G+C content of 54.0 mol%. The digital DDH and average nucleotide identity values between strain HYT19T and F. limi BUZ 3T were 28.8% and 85.1%, respectively. MK-7 was the sole respiratory quinone. The major polar lipids were phosphatidylethanolamine, unidentified aminophospholipid, two unidentified aminolipids, unidentified phospholipid and unidentified lipid. The strain contained C16:1ω5c, iso-C15:0, summed feature 3 (C16:1ω6c and/or C16:1ω7c), C16:0, iso-C17:0 3-OH and anteiso-C15:0 as the major fatty acids. On the basis of phylogenetic, genomic, phenotypic and chemotaxonomic analysis, we propose a new species Fibrisoma montanum sp. nov. of genus Fibrisoma. The type strain is HYT19T (= CCTCC AB 2018342T = JCM 33105T).

Sphingomonas gilva sp. nov., isolated from mountain soil.

A Gram-stain-negative, strictly aerobic, motile, yellow, rod-shaped bacterium, designated ZDH117T, was isolated from soilsampled atthe Danxialandformin Guangdong Province, PR China. The 16S rRNA gene sequence of strain ZDH117T had highest similarityvalues to Sphingomonas adhaesivaDSM 7418T (97.5 %), SphingomonasdesiccabilisCP1DT (97.3 %) and Sphingomonas ginsenosidimutans KACC 14949T (97.2 %). However, phylogenetic analyses based on 16S rRNA gene sequences demonstrated that strain ZDH117T clustered with Sphingomonas zeicaulis 541T (96.17 %) and Sphingomonas sanxanigenens DSM 19645T (95.95 %). The genomic average nucleotide identity values of ZDH117T with S. adhaesiva DSM 7418T, S. desiccabilis CP1DTand S. ginsenosidimutans KACC TT were 75.1, 75.2 and 75.0 %, respectively. The G+C content of the genomic DNA was 67.6 mol%. Strain ZDH117T was characterized to have ubiquinone-10 as the predominant respiratory quinone, sym-homospermidine as the major polyamine and summed feature 8 (C18 : 1ω6c and/or C18 : 1ω7c), C14 : 0-2OH, C16 : 0 and summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c) as the major cellular fatty acids (>5 % of total). The predominant polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, sphingoglycolipid, an unidentified phospholipid and three unidentified lipids. On the basis of its phenotypic, chemotaxonomic and phylogenetic characteristics, strain ZDH117T represents a novel species of the genus Sphingomonas, for which the name Sphingomonas gilva sp. nov. is proposed. The type strain is ZDH117T (=KCTC 62894T=CCTCCAB 2018262T).

Paenibacillus flagellatus sp. nov., isolated from selenium mineral soil.

Strain DXL2T, a Gram-stain-negative, rod-shaped, endospore-forming, motile, aerobic bacterium, was isolated from selenium mineral soil. DXL2T had the highest 16S rRNA gene sequence similarities with those of Paenibacillus ginsengarviGsoil 139T (96.8 %), Paenibacillushemerocallicola DLE-12T (95.5 %) and Paenibacillus hodogayensisSGT (95.4 %). The genome size of DXL2T was 7.24 Mb, containing 6243 predicted protein-coding genes, with a DNA G+C content of 60.2 mol%. DXL2T contained meso-diaminopimelic acid in the cell-wall peptidoglycan. The major cellular fatty acids were anteiso-C15 : 0, iso-C16 : 0 and iso-C15 : 0. The major quinone was menaquinone 7. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two aminophospholipids, an unidentified aminolipid, phosphatidylmethylethanolamine, an unidentified glycolipid and an unidentified phospholipid. Compared with the other strains, DXL2T had a specific phospholipid and a specific aminolipid, it hydrolyzed Tween 40 and could not assimilate potassium gluconate. On the basis of the phenotypic, chemotaxonomic and phylogenetic results, strain DXL2T represents a novel species within the genus Paenibacillus, for which the name Paenibacillusflagellatus sp. nov. is proposed. The type strain is DXL2T (=KCTC 33976T=CCTCC AB 2018054T).

Sphingomonas aracearum sp. nov., isolated from rhizospheric soil of Araceae plants.

A Gram-stain-negative, single polar flagellum bacterium, WZY27T, was isolated from rhizospheric soil of Araceae plants. The results of phylogenetic analysis based on 16S rRNA gene sequences showed that this strain is closely related to Sphingomonas adhaesiva DSM 7418T (97.2 % similarity), Sphingomonaskoreensis KCTC 2883 (97.1 %) and Sphingomonas ginsenosidimutans JCM 17074T (97.0 %). The genomic average nucleotide identity values between strain WZY27T and the above three strains were 75.3, 73.2 and 75.4 %, and the in silico DNA-DNA hybridization values were 19.1 , 20.1 and 20.9 %, respectively. The major fatty acids (>5 %) of strain WZY27T were summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c), C16 : 0, C14 : 0 2-OH and C18 : 1 ω7c 11-methyl. The predominant respiratory quinone and polyamine were ubiquinone Q-10 and homospermidine, respectively. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phospholipids, glycolipids, phosphatidylcholine and sphingoglycolipid. The G+C content of the genomic DNA was 68.4 mol%. Based on the results of genotypic, chemotaxonomic and phenotypic characterization, strain WZY27T represents a novel species of the genus Sphingomonas, for which the name Sphingomonas aracearum sp. nov. is proposed. The type strain is WZY27T (=KCTC 62523T=CCTCC AB 2018056T).

Efflux proteins MacAB confer resistance to arsenite and penicillin/macrolide-type antibiotics in Agrobacterium tumefaciens 5A.

Antibiotic and arsenic (As) contaminations are worldwide public health problems. Previously, the bacterial ABC-type efflux protein MacAB reportedly conferred resistance to macrolide-type antibiotics but not to other metal(loid)s. In this study, the roles of MacAB for the co-resistance of different antibiotics and several metal(loid)s were analyzed in Agrobacterium tumefaciens 5A, a strain resistant to arsenite [As(III)] and several types of antibiotics. The macA and macB genes were cotranscribed, and macB was deleted in A. tumefaciens 5A and heterologously expressed in Escherichia coli AW3110 and E. coli S17-1. Compared to the wild-type strain 5A, the macB deletion strain reduced bacterial resistance levels to several macrolide-type and penicillin-type antibiotics but not to cephalosporin-type antibiotics. In addition, the macB deletion strain showed lower resistance to As(III) but not to arsenate [As(V)], antimonite [Sb(III)] and cadmium chloride [Cd(II)]. The mutant strain 5A-ΔmacB cells accumulated more As(III) than the cells of the wild-type. Furthermore, heterologous expression of MacAB in E. coli S17-1 showed that MacAB was essential for resistance to macrolide, several penicillin-type antibiotics and As(III) but not to As(V). Heterologous expression of MacAB in E. coli AW3110 reduced the cellular accumulation of As(III) but not of As(V), indicating that MacAB is responsible for the efflux of As(III). These results demonstrated that, in addition to macrolide-type antibiotics, MacAB also conferred resistance to penicillin-type antibiotics and As(III) by extruding them out of cells. This finding contributes to a better understanding of the bacterial resistance mechanisms of antibiotics and metal(loid)s.

Nocardioides litorisoli sp. nov., isolated from lakeside soil.

A Gram-stain-positive, rod-shaped, non-spore-forming bacterium, designated as x-2T, was isolated from lakeside soil of Sayram in the Xinjiang Uygur Autonomous Region, PR China. On the basis of 16S rRNA gene sequences, strain x-2T belongs to the genus Nocardioides in the family Nocardioidaceae, being most closely related to Nocardioides panacisoli Gsoil 346T (97.36 % 16S rRNA gene sequence similarity). Strain x-2T was characterized chemotaxonomically and found to have ll-diaminopimelic acid in the cell-wall peptidoglycan, phosphatidylglycerol, diphosphatidylglycerol, glycolipids and another three unknown phospholipids as the major polar lipids, MK-8(H4) as the predominant menaquinone and C18 : 1ω9c, iso-C16 : 0, C17 : 1ω8c and C16 : 0 as the major fatty acids. The genomic DNA G+C content of the novel strain was 71.1 mol%. The level of DNA-DNA relatedness between strain x-2T and N. panacisoli KCTC 19470T (=Gsoil 346T) was 29.8 %. These chemotaxonomic characters support the position of strain x-2T within the genus Nocardioides. The results of physiological and biochemical tests, as well as phylogenetic analysis, suggest that strain x-2T represents a novel species of the genus Nocardioides, for which the name Nocardioides litorisoli sp. nov. is proposed. The type strain is x-2T (=KCTC 39845T=CCTCCAB 2016255T).

Domibacillus antri sp. nov., isolated from the soil of a cave.

A Gram-reaction-positive, strictly aerobic, capsule-forming, motile and rod-shaped bacterium, designated strain XD80T, was isolated from the soil of a native cave in Lichuan, Hubei province, China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain XD80T was most closely related to Domibacillus iocasae CCTCC AB 2015183T (98.66 % sequence similarity), followed by Domibacillus robiginosus DSM 25058T(97.83 %), Domibacillus tundrae KCTC 33549T (97.70 %), Domibacillus enclensis CCTCC AB 2011121T (97.21 %) and Domibacillus indicus DSM 28032T (96.96 %). Levels of DNA-DNA relatedness between strain XD80T and D. iocasae CCTCC AB 2015183T, D. robiginosusDSM 25058T, D. tundrae KCTC 33549T and D. enclensis CCTCC AB 2011121T were 37.4 %, 53.8 %, 53.6 % and 52.7 %, respectively. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, aminophospholipid and two unknown phospholipids. The predominant fatty acids (>5 %) were iso-C15 : 0 (37.3 %), anteiso-C15 : 0 (10.8 %), C16 : 0 (10.4 %), iso-C17 : 0 (10.3 %), C16 : 1ω11c (9.6 %) and anteiso-C17 : 0 (7.4 %). MK-6 (86.4 %) was the major respiratory quinone. The DNA G+C content was 46.4 mol%. The cell-wall peptidoglycan contained meso-diaminopimelic acid (type A1γ). Ribose and glucose were the major whole-cell sugars. In addition, strain XD80T showed differential physiological characteristics from most members of the genus Domibacillus, encompassing hydrolysis of starch, acid production from inositol and raffinose, and production of valine arylamidase. The results of this polyphasic study indicated that strain XD80T represents a novel species of the genus Domibacillus, for which the name Domibacillus antri sp. nov. is proposed. The type strain is XD80T (=CCTCC AB 2015053T=KCTC 33636T).

Hymenobacter monticola sp. nov., isolated from mountain soil.

A Gram-reaction-negative, aerobic, non-motile, red-pigmented and rod-shaped bacterium, designated XF-6RT, was isolated from mountain soil in the Sichuan province of China. Phylogenetic trees based on 16S rRNA gene sequence analysis showed that XF-6RT belonged to the genus Hymenobacter. The greatest 16S rRNA gene sequence similarities of strain XF-6RT were with Hymenobacter soli PB17T (96.4 %) and Hymenobacter saemangeumensis GSR0100T (95.8 %). Summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), iso-C15 : 0, C16 : 1ω5c and anteiso-C15 : 0 were the major fatty acids (>10 %). The only menaquinone was menaquinone-7. The major polar lipids were phosphatidylethanolamine, four aminolipids, four phosphoaminolipids and three lipids. The DNA G+C content was 62 mol%. On the basis of the polyphasic taxonomic analysis, strain XF-6RT is considered to represent a novel species of the genus Hymenobacter, for which the name Hymenobacter monticola sp. nov. is proposed. The type strain is XF-6RT ( = KCTC 42733T = CCTCC AB 2015206T).

Sphingoaurantiacus capsulatus sp. nov., isolated from mountain soil, and emended description of the genus Sphingoaurantiacus.

A novel Gram-stain-negative, strictly aerobic, non-motile, rod-shaped, capsule-forming bacterium, designated strain YLT33T, that formed orange-red colonies was isolated from mountain cliff soil from Enshi Grand Canyon, southwest China. Growth occurred at 4-35 °C (optimum 28 °C) and at pH 6.0-10.0 (optimum 7.0). It showed maximum (99.3 %) 16S rRNA gene sequence similarity and formed a monophyletic clade with Sphingoaurantiacus polygranulatusMC 3718T (=CCTCC 2014274T). The DNA G+C content was 68.5 mol% and strain YLT33T showed a 50.5 % DNA-DNA relatedness value to S. polygranulatusMC 3718T. The major fatty acids (>5 %) were C17 : 1ω6c (40.7 %), C15 : 0 (10.4 %), C15 : 1ω6c (9.4 %), summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH; 8.6 %), C17 : 1ω8c (7.1 %), C18 : 1ω7c (6.1 %), and C15 : 0 2-OH (5.7 %). Ubiquinone-10 was the sole respiratory quinone. The polar lipids of strain YLT33T contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, sphingoglycolipid, two unknown glycolipids and one unknown phospholipid. Carotenoids were present in cells. Homospermidine was the major polyamine. In addition, strain YLT33T showed obvious differences from the closely related strain S. polygranulatusMC 3718T with respect to major polar lipids, fatty acids and other morphological, physiological and biochemical characteristics. These results from polyphasic taxonomic studies reveal that strain YLT33T represents a novel species of the genus Sphingoaurantiacus, for which the name Sphingoaurantiacuscapsulatus sp. nov. is proposed. The type strain is YLT33T (=CCTCC AB 2015150T=KCTC 42644T).

Pedobacter vanadiisoli sp. nov., isolated from soil of a vanadium mine.

A Gram-stain-negative, light pink, non-motile, rod-shaped, aerobic bacterium, designated strain XNV015T, was isolated from soil of a vanadium mine. Phylogenetic analyses based on 16S rRNA gene sequences indicated that it belongs to the genus Pedobacter and was closely related to Pedobacter suwonensis DSM 18130T (96.93 % sequence similarity), Pedobacter alluvionis NWER-II11T (96.66 %), Pedobacter terrae DS-57T (96.54 %), Pedobacter kyungheensis KACC 16221T (96.54 %) and Pedobacter soli KACC 14939T (96.47 %). This strain clearly differed from the closely related species in terms of acid production from rhamnose and ethanol. Menaquinone-7 was the predominant respiratory quinone. The predominant fatty acids included iso-C15 : 0, C16 : 1ω5c, summed feature 3, iso-C17 : 0 3-OH and C17 : 0 2-OH. The major polar lipids were phosphatidylethanolamine, glycolipids, lipids and aminolipids. The genomic DNA G+C content was 43.8 mol%. The genotypic analysis, biochemical properties, and phenotypic and chemotaxonomic characteristics indicate that strain XNV015T represents a novel species of the genus Pedobacter, for which the name Pedobacter vanadiisoli sp. nov. is proposed. The type strain is XNV015T (=CCTCC AB 2015319T=KCTC 42866T).

Flavihumibacter stibioxidans sp. nov., an antimony-oxidizing bacterium isolated from antimony mine soil.

A Gram-stain-positive, strictly aerobic, non-motile and rod-shaped bacterial strain, designated YS-17T, was isolated from soil in the Lengshuijiang antimony mine, Hunan Province, China. Comparative 16S rRNA gene sequencing analysis clustered it with Flavihumibacter strains, and strain YS-17T was most closely related to Flavihumibacter cheonanensis WS16T (97.2 % similarity), Flavihumibacter petaseus T41T (96.6 %) and Flavihumibacter solisilvae 3-3T (96.5 %). The level of DNA-DNA relatedness between strain YS-17T and F. cheonanensis JCM 19322T was 35.5±0.1 % (n=2). The major respiratory quinone of strain YS-17T was menaquinone-7 and the major polar lipids were phosphatidylethanolamine, two unidentified lipids, two unidentified amino lipids and phospholipid. The major fatty acids (≥5 %) were iso-C15 : 0, iso-C15 : 1 G, unknown ECL 13.565, iso-C17 : 0 3-OH, C15 : 0, C16 : 1ω5c and anteiso-C15 : 0. The DNA G+C content was 47.8 mol%. Compared with other Flavihumibacter strains, strain YS-17T showed major biophysical and biochemical differences, with the ability to hydrolyse gelatin and to assimilate salicin and l-proline. The results demonstrated that strain YS-17T belongs to the genus Flavihumibacter and represents a novel species, for which the name Flavihumibacter stibioxidans sp. nov. is proposed. The type strain is YS-17T (=CCTCC AB 2016053T=KCTC 52205T).

Reduction of selenite to Se(0) nanoparticles by filamentous bacterium Streptomyces sp. ES2-5 isolated from a selenium mining soil.

BACKGROUND: Selenium (Se) is an essential trace element in living systems. Microorganisms play a pivotal role in the selenium cycle both in life and in environment. Different bacterial strains are able to reduce Se(IV) (selenite) and (or) Se(VI) (selenate) to less toxic Se(0) with the formation of Se nanoparticles (SeNPs). The biogenic SeNPs have exhibited promising application prospects in medicine, biosensors and environmental remediation. These microorganisms might be explored as potential biofactories for synthesis of metal(loid) nanoparticles. RESULTS: A strictly aerobic, branched actinomycete strain, ES2-5, was isolated from a selenium mining soil in southwest China, identified as Streptomyces sp. based on 16S rRNA gene sequence, physiologic and morphologic characteristics. Both SEM and TEM-EDX analysis showed that Se(IV) was reduced to Se(0) with the formation of SeNPs as a linear chain in the cytoplasm. The sizes of the SeNPs were in the range of 50-500 nm. The cellular concentration of glutathione per biomass decreased along with Se(IV) reduction, and no SeNPs were observed in different sub-cellular fractions in presence of NADPH or NADH as an electron donor, indicating glutathione is most possibly involved in vivo Se(IV) reduction. Strain ES2-5 was resistant to some heavy metal(loid)s such as Se(IV), Cr(VI) and Zn(II) with minimal inhibitory concentration of 50, 80 and 1.5 mM, respectively. CONCLUSIONS: The reducing mechanism of Se(IV) to elemental SeNPs under aerobic condition was investigated in a filamentous strain of Streptomyces. Se(IV) reduction is mediated by glutathione and then SeNPs synthesis happens inside of the cells. The SeNPs are released via hypha lysis or fragmentation. It would be very useful in Se bioremediation if Streptomyces sp. ES2-5 is applied to the contaminated site because of its ability of spore reproduction, Se(IV) reduction, and adaptation in soil.

Chitinophaga barathri sp. nov., isolated from mountain soil.

A Gram-stain-negative, non-motile, rod-shaped, aerobic bacterium, designated strain YLT18T, was isolated from mountain cliff soil of Enshi Grand Canyon in China. The major menaquinone was menaquinone 7 (MK-7) and the predominant fatty acids (>5 %) were iso-C15 : 0, C16 : 1ω5c, iso-C17 : 0 3-OH, summed feature 3 (C16 : 1ω7c/iso-C15 : 0 2-OH) and iso-C15 : 0 3-OH. The major polar lipids were phosphatidylethanolamine, two unknown aminophospholipids, two unknown aminolipids and two unknown polar lipids. The DNA G+C content was 55.4 mol%. According to phylogenetic analysis based on 16S rRNA gene sequences, strain YLT18T was related most closely to Chitinophaga niabensis JS13-10T ( = DSM 24787T) and Chitinophaga cymbidii R156-2T ( = KCTC 23738T), with similarities of 96.7 and 96.2 %, respectively. In addition, strain YLT18T showed obvious differences from the closely related species in terms of esterase (C4) activity, acid production from fructose and rhamnose, and sole carbon source utilization by arabinose and rhamnose. The results from this polyphasic taxonomic study revealed that strain YLT18T represents a novel species of the genus Chitinophaga, for which the name Chitinophaga barathri sp. nov. is proposed. The type strain is YLT18T ( = KCTC 42472T = CCTCC AB 2015054T).

Selenite reduction by the obligate aerobic bacterium Comamonas testosteroni S44 isolated from a metal-contaminated soil.

BACKGROUND: Selenium (Se) is an essential trace element in most organisms but has to be carefully handled since there is a thin line between beneficial and toxic concentrations. Many bacteria have the ability to reduce selenite (Se(IV)) and (or) selenate (Se(VI)) to red elemental selenium that is less toxic. RESULTS: A strictly aerobic bacterium, Comamonas testosteroni S44, previously isolated from metal(loid)-contaminated soil in southern China, reduced Se(IV) to red selenium nanoparticles (SeNPs) with sizes ranging from 100 to 200 nm. Both energy dispersive X-ray Spectroscopy (EDX or EDS) and EDS Elemental Mapping showed no element Se and SeNPs were produced inside cells whereas Se(IV) was reduced to red-colored selenium in the cytoplasmic fraction in presence of NADPH. Tungstate inhibited Se(VI) but not Se(IV) reduction, indicating the Se(IV)-reducing determinant does not contain molybdenum as co-factor. Strain S44 was resistant to multiple heavy and transition metal(loid)s such as Se(IV), As(III), Cu(II), and Cd(II) with minimal inhibitory concentrations (MIC) of 100 mM, 20 mM, 4 mM, and 0.5 mM, respectively. Disruption of iscR encoding a transcriptional regulator negatively impacted cellular growth and subsequent resistance to multiple heavy metal(loid)s. CONCLUSIONS: C. testosteroni S44 could be very useful for bioremediation in heavy metal(loid) polluted soils due to the ability to both reduce toxic Se(VI) and Se(IV) to non-toxic Se (0) under aerobic conditions and to tolerate multiple heavy and transition metals. IscR appears to be an activator to regulate genes involved in resistance to heavy or transition metal(loid)s but not for genes responsible for Se(IV) reduction.

Paenirhodobacter enshiensis gen. nov., sp. nov., a non-photosynthetic bacterium isolated from soil, and emended descriptions of the genera Rhodobacter and Haematobacter.

A Gram-reaction-negative, facultatively anaerobic, non-motile, rod-shaped, non-photosynthetic bacterial strain, DW2-9(T), was isolated from soil. The highest 16S rRNA gene sequence similarities were found to Rhodobacter capsulatus ATCC 11166(T) (97.1%), Rhodobacter viridis JA737(T) (96.4%), Rhodobacter maris JA276(T) (96.2%), Rhodobacter veldkampii ATCC 35703(T) (96.0%), Haematobacter massiliensis CCUG 47968(T) (96.0%), Haematobacter missouriensis CCUG 52307(T) (95.9%) and Rhodobacter aestuarii JA296(T) (95.7%). The genomic DNA G+C content was 67.2 mol% and the major respiratory quinone was ubiquinone 10 (Q-10). The major cellular fatty acids (>5%) were C(18 : 1)ω7c, C(16 : 0), C(19 : 0) cyclo ω8c and summed feature 3 (one or more of iso-C(15 : 0) 2-OH, C(16 : 1)ω6c and C(16 : 1)ω7c). However, unlike species of the genus Rhodobacter, strain DW2-9(T) neither formed internal photosynthetic membranes nor produced photosynthetic pigments. DNA-DNA hybridization between strain DW2-9(T) and R. capsulatus JCM 21090(T) showed a relatedness of 33%. Strain DW2-9(T) contained phosphatidylethanolamine, phosphatidylglycerol and an unknown aminophospholipid as major polar lipids, which differed from those of species of the genera Rhodobacter and Haematobacter. In addition to the differences in phylogenetic position and polar lipid types, strain DW2-9(T) could be distinguished from species of the genus Haematobacter by the cultivation conditions. On the basis of our polyphasic taxonomic analysis, strain DW2-9(T) is considered to represent a novel genus and species, for which the name Paenirhodobacter enshiensis gen. nov., sp. nov. is proposed. The type strain of Paenirhodobacter enshiensis is DW2-9(T) ( = CCTCC AB 2011145(T) = KCTC 15169(T)). Emended descriptions of the genera Rhodobacter and Haematobacter are also proposed.